Source of Inhibin in Ovine Fetal Plasma and Amniotic Fluid during Late Gestation: Half-Life of Fetal Inhibin1

Abstract

Immunoactive inhibin (ir-inhibin) concentrations were determined in chronically catheterized sheep between 120 and 145 days gestation. Maternal plasma ir-inhibin concentrations remained basal (0.19 +/- 0.05 ng/ml) throughout the period of study. Immunoactive inhibin concentrations in male and female fetal plasma were elevated above those observed in maternal plasma, with the concentrations in plasma of male fetuses (7.38 +/- 0.04 ng/ml) being significantly greater (p < 0.001) than those in female fetuses (1.07 +/- 0.14 ng/ml). The concentrations of ir-inhibin in amniotic fluid of ewes bearing male fetuses (10.93 +/- 1.55 ng/ml) were significantly greater than in ewes bearing female fetuses (2.81 +/- 0.32 ng/ml; p < 0.05) but not significantly different from the concentrations in male fetal plasma. Immunoactive inhibin concentrations decreased following surgery in gonadectomized fetuses, to 3.25 +/- 0.99 ng/ml within 6 h, and remained at a mean value of 0.75 +/- 0.38 ng/ml from 24 h after gonadectomy. The half-life of circulating inhibin in fetal plasma, estimated from the decay curve during the first 6 h after surgery, was 3.94 +/- 0.88 h. There was a significant (p < 0.05) decrease in the concentration of ir-inhibin in amniotic fluid after gonadectomy; however, this decrease occurred gradually over 7 days, and ir-inhibin concentrations did not fall to those concentrations observed in fetal circulation at any time after gonadectomy. It is concluded that the major source of circulating ir-inhibin in male fetal plasma, but not in amniotic fluid, is the gonads.

Localization and Secretion of Inhibins in the Equine Fetal Ovaries1

“…Circulating concentrations of ir-inhibin in both male and female ovine fetuses have been reported to be higher than those in maternal circulation [17,19]. It was reported that gonadectomy in the fetus caused a rapid decline in circulating ir-inhibin levels, suggesting that the gonads were the primary source of circulating ir-inhibin [19].…”

“…It was reported that gonadectomy in the fetus caused a rapid decline in circulating ir-inhibin levels, suggesting that the gonads were the primary source of circulating ir-inhibin [19]. The equine fetal gonads of both sexes have attracted much interest because of the remarkable enlargement in size as a result of massive number of interstitial cells between the third and ninth months of gestation [38,39].…”

“…Granulosa cells of various sized follicles and theca cells of large follicles are the primary sources of inhibin during the estrous cycle of the mare [15][16][17]. Inhibin production in fetal ovaries has been studied in sheep [18][19][20], cows [21], monkeys [22], and humans [22]. A previous study by our laboratory [23,24] and a study by others [25] have documented inhibin secretion and the localization of inhibin ␣ subunit mRNA, respectively, in the fetal ovaries.…”

Changes in Inhibin Secretion during Development of the Female Duck Embryo

“…The adrenal gland has been postulated to be a main source of circulating inhibin in the chicken embryo (Rombauts et al, 1994). With respect to mammals, the fetal gonad is likely to be a major source of inhibin in male but not in female ovine fetal plasma (Miller et al, 1997). In the male ovine fetus, gonadectomy considerably decrease fetal circulating inhibin.…”

Inter-relationships among gonadotrophins, reproductive steroids and inhibin in freemartin ewes

“…Concentrations of progesterone were measured by the ELISA method described by Groves et al (1990). Concentrations of inhibin were determined using the method of Beard et al (1990), modified by using the antiserum prepared by Robertson et al (1989) and validated for use in sheep by Miller et al (1997). Details of reagents and assay validation criteria for each of these assays are given (Table 1).…”